Avis poor customer service and Taking money from Customers accounts without permission

I had a bad experience with Avis (Menlyn) on the 26 June.I rented a car for a month then the money that was held in my account was R11800,which includes the deposit.I was supposed to return the car on the 26July.Then on the 26July I went to Avis and asked them to extend my rental with 7days.Then they said I must pay R2200 and they will have to swipe R2000 again for the deposit.When I returned the car I didn't get any of my deposit back.Then on the 1st of August Avis went further to debit my account and they took R8250,Then on the 18/08 they took R2400 and R2000 without my permission.I immediately complained to Avis customer Service and the only thing that I get from them is they are still waiting for a feedback from Avis Menlyn branch.